Skin Infections Flashcards
How does Staphylococcus confer Pathogenic properties?
Staphylococcus aureus expresses virulence factors that confer pathogenic properties
What are some diseases caused by Staphylococcus?
Ecthyma
Impetigo
Cellulitis
Folliculitis
- Furunculosis
- Carbuncles
Staphylococcal scalded skin syndrome (SSSS)
Superinfects other dermatoses (e.g. atopic eczema, HSV, leg ulcers)
How does Streptococcus confer Virulence?
Strepococcus pyogenes (β-haemolytic) attaches to epithelial surfaces via lipoteichoic acid portion of fimbriae
- Has M protein (anti-phagocytic) & hyaluronic acid capsule - Produces erythrogenic exotoxins - Produces streptolysins S and O
What are some conditions caused by Streptococcus?
Ecthyma
Cellulitis
Impetigo
Erysipelas
Scarlet fever
Necrotizing fasciitis
Superinfects other dermatoses (e.g. leg ulcers)
How does Folliculitis present?
Follicular erythema; sometimes pustular.
May be infectious or non-infectious.
What is Eosonophilic/non-infectious Folliculitis associated with?
HIV
What is a possible cause of recurrent folliculitis?
Recurrent cases may arise from nasal carriage of Staphylococcus aureus, particularly strains expressing Panton-Valentine leukocidin (PVL).
What is the treatment for Folliculitis?
Antibiotics (usually flucloxacillin or erythromycin)
Incision and drainage is required for furunculosis
What is the difference between a furuncle and a carbuncle?
A furuncle is a deep follicular abscess
- Involvement with adjacent connected follicles
= Carbuncle.
Carbuncle - more likely to lead to complications such as cellulitis and septicaemia
Why do some patients develop recurrent staphylococcal impetigo or recurrent furunculosis?
Establishment as a part of the resident microbial flora
- Abundant in nasal flora
Immune deficiency
- Hypogammaglobulinaemia
- HyperIgE syndrome – deficiency - Chronic granulomatous disease
- AIDS
- Diabetes Mellitus
What happens in Panton Valentine Leukocidin PVL Staphylococcus Aureus
β-pore-forming exotoxin
Leukocyte destruction and tissue necrosis
Higher morbidity, mortality and transmissibility
Skin
- Recurrent and painful abscesses
- Folliculitis
- Cellulitis
- Often painful, more than 1 site, recurrent, present in contacts
Extracutaneous:
- Necrotising pneumonia
- Necrotising fasciitis
- Purpura fulminansWhat are the five C’s of PVL?
Close Contact – e.g. hugging, contact sports
Contaminated items , e.g. gym equipment, towels or razors.
Crowding –crowded living conditions such as e.g. military accommodation, prisons and boarding schools.
Cleanliness (of environment)
Cuts and grazes – having a cut or graze will allow the bacteria to enter the body
What is the treatment for PVL?
Consult local microbiologist / guidelines
Antibiotics (often tetracycline)
Decolonisation – often:
- Chlorhexidine body wash for 7 days
- Nasal application of mupirocin ointment 5 days)
Treatment of close contacts
What happens in Pseudomonal Folliculitis?
Associated with hot tub use, swimming pools and depilatories, wet suit
Appears 1-3 days after exposure, as a diffuse truncal eruption.
Follicular erythematous papule
Rarely: abscesses, lymphangitis and fever.
Most cases self-limited – no treatment required.
Severe or recurrent cases can be treated with oral ciprofloxacin
What happens in Cellulitis?
Infection of lower dermis and subcutaneous tissue
Tender swelling with ill-defined, blanching erythema or oedema
Most cases: Streptococcus pyogenes & Staphylococcus aureus
Oedema is a predisposing factor
How do you treat Cellulitis?
Systemic Antibiotics
What happens in Impetigo?
Superficial bacterial infection, stuck-on, honey-coloured crusts overlying an erosion.
Caused by
- Streptococci (non-bullous)
or
- Staphylococci (bullous)
Caused by exfoliative toxins A & B, split epidermis by targeting desmoglein I.
Often affects face (perioral, ears, nares).
Treated with topical +/- systemic antibiotics.
Where does Impetiginisation occur?
Occurs in atopic dermatitis
- Gold crust - Staphylococcus aureus
What happens in Ecthyma?
Severe form of streptococcal impetigo
Thick crust overlying a punch out ulceration surrounded by erythema
Usually on lower extremities
What is Staphylococcal Skin Syndrome?
Neonates, infants or immunocompromised adults
Due to exfoliative toxin
Infection occurs at distant site (ie conjunctivitis or abscess
∴ Organism cannot be cultured from denuded skin.
In neonates, kidneys cannot excrete the exfoliative toxin quickly
→ Diffuse tender erythema that
→ Rapid progression to flaccid bullae,
→ Wrinkle and exfoliate, leaving oozing, erythematous base
Clinically resembles Stevens-Johnson syndrome / toxic epidermal necrolysis
What happens in Toxic Shock syndrome?
Febrile illness due to Group A Staphylococcus aureus strain that produces pyrogenic exotoxin TSST-1 Fever >38.9°C Hypotension Diffuse erythema Involvement of ≥ systems: – Gastrointestinal – Muscular – CNS - Renal - Hepatic Mucous membranes (erythema) Hematologic (platelets <100 000/mm3) Desquamation predominantly of palms and soles 1-2 weeks after resolution of erythema
What is Erythrasma?
Infection of Corynebacterium minutissimum
Well demarcated patches in intertriginous areas
- initially pink
- Become brown and scaly
What is Pitted Keratolysis?
Pitted erosions of soles
Caused by Corynebacteria
Treated with topical clindamycin
What happens in Erysipeloid?
Erythema and oedema of the hand after handling contaminated raw fish or meat.
Extends slowly over weeks.
Erysipelothrix rhusiopathiae
What happens in Anthrax?
Painless necrotic ulcer with surrounding oedema and regional lymphadenopathy (with pain in lymph nodes) at the site of contact with hides, bone meal or wool infected with Bacillus anthracis.
What happens in Blistering Distal Dactylitis?
Rare infection caused by Streptococcus pyogenes or Staphylococcus aureus
Typically - young children
1 or more tender superficial bullae on erythematous base on the volar fat pad of a finger
Toes may rarely be affected
What happens in Erysipelas?
Infection of deep dermis and subcutis
Caused by β-haemolytic streptococci or Staphylococcus aureus
Painful
Prodrome of malaise, fever, headache.
Presents as erythematous indurated plaque with a sharply demarcated border and a cliff-drop edge
+/- blistering
Face or limb
+/- red streak of lymphangitis and local lymphadenopathy.
Portal of entry must be sought (e.g. tinea pedis).
Systemic symptoms (fever, malaise).
Treated with intravenous antibiotics.
What happens in Scarlet Fever?
Primarily a disease of children
Caused by upper respiratory tract infection with erythrogenic toxin-producing Streptococcus pyogenes
Preceded by sore throat, headache, malaise, chills, anorexia and fever
Eruption begins 12-48 hours later
- Blanchable tiny pinkish-red spots on chest, neck and axillae
- Spread to whole body within 12 hours
- Sandpaper-like texture
Complications: otitis, mastoiditis, sinusitis, pneumonia, myocarditis, hepatitis, meningitis, rheumatic fever, acute glomerulonephritis
What happens in Necrotising Fasciitis?
Initial dusky induration (usually of a limb), followed by rapid painful necrosis of skin, connective tissue and muscle.
Potentially fatal
Usually synergistic: streptococci, staphylococci, enterobacteriaceae and anaerobes.
Prompt diagnosis essential (requires high index of suspicion), followed by broad-spectrum parenteral antibiotics and surgical debridement.
MRI can aid diagnosis.
Blood and tissue cultures can determine organisms and sensitivities.
Mortality is high.
Can affect the scrotum (Fournier’s gangrene).
What happens in Atypical Mycobacterium Infection?
Important cause of infection in immunosuppressed states.
Mycobacterium marinum causes indolent granulomatous ulcers (fish-tank granuloma) in healthy people
- Sporotrichoid (lymph node) spread
Mycobacterium chelonae & abscessus - puncture wounds, tattoos, skin trauma or surgery
Mycobacterium ulcerans: an important cause of limb ulceration in Africa (Buruli ulcer) or Australia (Searle’s ulcer
What happens in Borreliosis/Lyme disease?
Annular erythema develops at site of the bite of a Borrelia-infected tick
Bite form Ixodes tick infected with Borrelia burgdorferi
Initial cutaneous manifestation: Erythema migrans (only in 75%)
- Erythematous papule at the bite site
- Progression to annular erythema of >20cm
What happens 1-30 days after infection in Lyme disease?
1-30 days after infection, fever, headache
Multiple secondary lesions develop - similar but smaller to initial lesion
Neuroborreliosis
- Facial palsy / other CN palsies
- Aseptic meningitis
- Polyradiculitis
Arthritis – painful and swollen large joints (knee is the most affected join)
Carditis
What happens in Tularaemia?
Caused by Francisella tularensis
Acquired through:
- Handling infected animals (squirrels and rabbits)
- Tick bites
- Deerfly bites
Ulceroglandular form
Primary skin lesion is small papules at inoculation site that rapidly necroses – leading to painful ulceration
+/- local cellulitis
Painful regional lymphadenopathy
Systemic symptoms: fever, chills, headache and malaise
What is the Problem with diagnosing Lyme disease?
Serology not sensitive
Histopathology - non-specific
High index of suspicion required for diagnosis
What happens in Ecthyma Gangrenosum?
Pseudomonas aeruginosa Usually occurs in neutropaenic patients Red macule(s) → oedematous → haemorrhagic bullae. May ulcerate in late stages or form an eschar surrounded by erythema
What are some different diagnoses for Escharotic Lesions?
Pseudomonas aeruginosa Usually occurs in neutropaenic patients Red macule(s) → oedematous → haemorrhagic bullae. May ulcerate in late stages or form an eschar surrounded by erythema
